[en] Post-mortem studies of Down syndrome (DS) individuals older than 35 years show that almost 100% of them develop the neuropathological symptoms of Alzheimer disease (AD). A test battery designed to assess several domains of cognition was administered to a group of 12 DS individuals older than 35 years. It proved sensitive to individual differences and thus appears to be appropriate for the observation of cognitive change linked to age. Statistical analyses do not reveal cognitive changes in the DS subjects after one year time. However qualitative analyses of individual profiles suggest a cognitive decline in one subject. Additionally, in a PET-scan examination, three subjects present a mild decrease in cerebral glucose metabolism similar to that usually observed in AD. An AD diagnostic though remains uncertain at this stage.